Sheets of resinous composition have found widespread use as decorative and wear-resistant coverings for a wide range of products. Such sheets, for example, are used extensively as wall, floor and table coverings, book covers, decorative containers, as fabrics for use as upholstery, clothing and automobile interiors, and the like. In many instances, the resinous composition sheets are applied or formed on backings such as woven fabrics, paper, felt, metal, wood, glass, and the like. These backing materials have many purposes, the most common being added strength and serviceability. It is common practice to emboss the surface of such sheets to give added-decorative appeal and, in many instances, further utility. Typical of the types of embossings are those which simulate leather or textured cloth, such as linen. In some instances, the embossed areas are filled in with pigmented ink by techniques known as "spanishing" or "valley printing."
The introduction of cellular resinous compositions has led to their incorporation in products such as recited above, either alone, or in combination with non-cellular resinous composition surface wear layers and/or backing webs. The cellular foam sheet gives the product various desirable properties, depending on the type of cellular foam, such as high resiliency and good feel or "hand."
Embossing of resinous composition sheets is conventionally accomplished with an embossing roll or plate which has been engraved or otherwise treated to create the design desired in raised relief on its surface. The sheet and/or embossing surface is heated and the design pressed into the heat-softened sheet.
Various methods have been suggested for producing cellular foam products having a textured or embossed surface without utilizing embossing rolls. Embossing rolls are expensive to produce and when combined with a valley printing operation are difficult to control. In some instances, it is desired to print a design and then emboss in register with the design. Such an operation requires very complex equipment. Additionally, embossing of curved or irregular surfaces is very difficult.
One method which eliminates embossing rolls is disclosed in U.S. Pat. No. 2,961,332 which issued to R. Frank Nairn on Nov. 22, 1960. In accordance with this patent, a layer of foamable resinous composition is formed on a base by printing a number of different resinous compositions each containing its own amount or type of blowing agent. The layer is then heated to decompose the blowing agent and fuse the composition. The product has an irregular or textured surface conforming to the amount or type of blowing agent in the various printed compositions. Another method is disclosed in U.S. Pat. No. 2,964,799 which issued to P. E. Roggi et al., on Dec. 20, 1960. According to this patent, a foamable resinous composition is formed into a self-supporting sheet of fused composition. Heat is then applied to the foamable composition sheet at various points to cause the blowing agent at those points to decompose and form a cellular structure. The raised areas in the finished sheet correspond to the points of heat application. U.S. Pat. No. 2,825,282 which issued to J. B. Gergen et al., on Mar. 4, 1958, discloses a related method for producing a letterpress makeready. In accordance with this latter patent, a foamable composition is formed into a sheet and then printed with inks containing radiant energy-absorbing pigments. On exposure of the sheet to radiant energy, the blowing agent in contact with the pigments receives more intense heat and, therefore, will decompose and form cellular foam without affecting the unprinted portions of the sheet. As is apparent, the heating must be very rapid and carefully controlled.
An embossing technique which has become known as chemical embossing and which has proven to be a vast improvement over the procedures of the prior art is disclosed in U.S. Pat. Nos. 3,293,094 and 3,093,108, which issued to R. Frank Nairn et al on Dec. 20, 1966. In this procedure, the decomposition temperature of a chemical blowing agent dispersed in a resinous polymer composition is controlled by applying an inhibitor to the surface of the composition. The subsequent application of heat selectively decomposes the blowing agent, thereby resulting in the formation of either depressed or raised areas in the final product at the points of inhibitor application. The vehicle for applying the inhibitor to the surface of the resinous composition is a liquid printing composition. The inhibitor is mixed with the printing composition so that after the product is heated the embossed areas are in register with the printed design.